During the development of new features or bug fixes, it would be extremely convenient to use Sandboxes as testing environments. Currently, this is only possible through Preview mode deployments.

This creates the need for an additional environment where developers can run initial tests before 'releasing' the feature in beta and testing it through Preview mode.

It would be very useful to be able to upload and install these 'development' versions directly into Sandboxes, just like we do with PTE apps, with the constraint (which already exists) that such environments can never be converted into production environments.

This solution would bring benefits to everyone:

1. For partners and developers: because it would speed up the update process, eliminating the waiting time tied to AppSource publication and validation.
2. For Microsoft: because it would reduce the server workload associated with handling submissions and publications.

This solution should only be intended for development and debugging purposes and not as a way to patch environments, exactly as it is for Preview versions.